/* Part of SWI-Prolog
Author: Tom Schrijvers, Markus Triska and Jan Wielemaker
E-mail: Tom.Schrijvers@cs.kuleuven.ac.be
WWW: http://www.swi-prolog.org
Copyright (c) 2004-2016, K.U.Leuven
All rights reserved.
Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions
are met:
1. Redistributions of source code must retain the above copyright
notice, this list of conditions and the following disclaimer.
2. Redistributions in binary form must reproduce the above copyright
notice, this list of conditions and the following disclaimer in
the documentation and/or other materials provided with the
distribution.
THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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*/
:- module(dif,
[ dif/2 % +Term1, +Term2
]).
:- autoload(library(lists),[append/3,reverse/2]).
:- set_prolog_flag(generate_debug_info, false).
/** <module> The dif/2 constraint
*/
%! dif(+Term1, +Term2) is semidet.
%
% Constraint that expresses that Term1 and Term2 never become
% identical (==/2). Fails if `Term1 == Term2`. Succeeds if Term1
% can never become identical to Term2. In other cases the
% predicate succeeds after attaching constraints to the relevant
% parts of Term1 and Term2 that prevent the two terms to become
% identical.
dif(X,Y) :-
X \== Y,
dif_c_c(X,Y,_).
dif_unifiable(X, Y, Us) :-
( current_prolog_flag(occurs_check, error) ->
catch(unifiable(X,Y,Us), error(occurs_check(_,_),_), false)
; unifiable(X, Y, Us)
).
dif_c_c(X,Y,OrNode) :-
( dif_unifiable(X, Y, Unifier) ->
( Unifier == [] ->
or_one_fail(OrNode)
;
dif_c_c_l(Unifier,OrNode)
)
;
or_succeed(OrNode)
).
dif_c_c_l(Unifier,OrNode) :-
length(Unifier,N),
extend_ornode(OrNode,N,List,Tail),
dif_c_c_l_aux(Unifier,OrNode,List,Tail).
extend_ornode(OrNode,N,List,Vars) :-
( get_attr(OrNode,dif,Attr) ->
Attr = node(M,Vars),
O is N + M - 1
;
O = N,
Vars = []
),
put_attr(OrNode,dif,node(O,List)).
dif_c_c_l_aux([],_,List,List).
dif_c_c_l_aux([X=Y|Unifier],OrNode,List,Tail) :-
List = [X=Y|Rest],
add_ornode(X,Y,OrNode),
dif_c_c_l_aux(Unifier,OrNode,Rest,Tail).
add_ornode(X,Y,OrNode) :-
add_ornode_var1(X,Y,OrNode),
( var(Y) ->
add_ornode_var2(X,Y,OrNode)
;
true
).
add_ornode_var1(X,Y,OrNode) :-
( get_attr(X,dif,Attr) ->
Attr = vardif(V1,V2),
put_attr(X,dif,vardif([OrNode-Y|V1],V2))
;
put_attr(X,dif,vardif([OrNode-Y],[]))
).
add_ornode_var2(X,Y,OrNode) :-
( get_attr(Y,dif,Attr) ->
Attr = vardif(V1,V2),
put_attr(Y,dif,vardif(V1,[OrNode-X|V2]))
;
put_attr(Y,dif,vardif([],[OrNode-X]))
).
attr_unify_hook(vardif(V1,V2),Other) :-
( var(Other) ->
reverse_lookups(V1,Other,OrNodes1,NV1),
or_one_fails(OrNodes1),
get_attr(Other,dif,OAttr),
OAttr = vardif(OV1,OV2),
reverse_lookups(OV1,Other,OrNodes2,NOV1),
or_one_fails(OrNodes2),
remove_obsolete(V2,Other,NV2),
remove_obsolete(OV2,Other,NOV2),
append(NV1,NOV1,CV1),
append(NV2,NOV2,CV2),
( CV1 == [], CV2 == [] ->
del_attr(Other,dif)
;
put_attr(Other,dif,vardif(CV1,CV2))
)
;
verify_compounds(V1,Other),
verify_compounds(V2,Other)
).
remove_obsolete([], _, []).
remove_obsolete([N-Y|T], X, L) :-
( Y==X ->
remove_obsolete(T, X, L)
; L=[N-Y|RT],
remove_obsolete(T, X, RT)
).
reverse_lookups([],_,[],[]).
reverse_lookups([N-X|NXs],Value,Nodes,Rest) :-
( X == Value ->
Nodes = [N|RNodes],
Rest = RRest
;
Nodes = RNodes,
Rest = [N-X|RRest]
),
reverse_lookups(NXs,Value,RNodes,RRest).
verify_compounds([],_).
verify_compounds([OrNode-Y|Rest],X) :-
( var(Y) ->
true
; OrNode == (-) ->
true
;
dif_c_c(X,Y,OrNode)
),
verify_compounds(Rest,X).
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
or_succeed(OrNode) :-
( attvar(OrNode) ->
get_attr(OrNode,dif,Attr),
Attr = node(_Counter,Pairs),
del_attr(OrNode,dif),
OrNode = (-),
del_or_dif(Pairs)
;
true
).
or_one_fails([]).
or_one_fails([N|Ns]) :-
or_one_fail(N),
or_one_fails(Ns).
or_one_fail(OrNode) :-
( attvar(OrNode) ->
get_attr(OrNode,dif,Attr),
Attr = node(Counter,Pairs),
NCounter is Counter - 1,
( NCounter == 0 ->
fail
;
put_attr(OrNode,dif,node(NCounter,Pairs))
)
;
fail
).
del_or_dif([]).
del_or_dif([X=Y|Xs]) :-
cleanup_dead_nodes(X),
cleanup_dead_nodes(Y),
del_or_dif(Xs).
cleanup_dead_nodes(X) :-
( attvar(X) ->
get_attr(X,dif,Attr),
Attr = vardif(V1,V2),
filter_dead_ors(V1,NV1),
filter_dead_ors(V2,NV2),
( NV1 == [], NV2 == [] ->
del_attr(X,dif)
;
put_attr(X,dif,vardif(NV1,NV2))
)
;
true
).
filter_dead_ors([],[]).
filter_dead_ors([Or-Y|Rest],List) :-
( var(Or) ->
List = [Or-Y|NRest]
;
List = NRest
),
filter_dead_ors(Rest,NRest).
/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
The attribute of a variable X is vardif/2. The first argument is a
list of pairs. The first component of each pair is an OrNode. The
attribute of each OrNode is node/2. The second argument of node/2
is a list of equations A = B. If the LHS of the first equation is
X, then return a goal, otherwise don't because someone else will.
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
attribute_goals(Var) -->
( { get_attr(Var, dif, vardif(Ors,_)) } ->
or_nodes(Ors, Var)
; or_node(Var)
).
or_node(O) -->
( { get_attr(O, dif, node(_, Pairs)) } ->
{ eqs_lefts_rights(Pairs, As, Bs) },
mydif(As, Bs),
{ del_attr(O, dif) }
; []
).
or_nodes([], _) --> [].
or_nodes([O-_|Os], X) -->
( { get_attr(O, dif, node(_, Eqs)) } ->
( { Eqs = [LHS=_|_], LHS == X } ->
{ eqs_lefts_rights(Eqs, As, Bs) },
mydif(As, Bs),
{ del_attr(O, dif) }
; []
)
; [] % or-node already removed
),
or_nodes(Os, X).
mydif([X], [Y]) --> !, dif_if_necessary(X, Y).
mydif(Xs0, Ys0) -->
{ reverse(Xs0, Xs), reverse(Ys0, Ys), % follow original order
X =.. [f|Xs], Y =.. [f|Ys] },
dif_if_necessary(X, Y).
dif_if_necessary(X, Y) -->
( { dif_unifiable(X, Y, _) } ->
[dif(X,Y)]
; []
).
eqs_lefts_rights([], [], []).
eqs_lefts_rights([A=B|ABs], [A|As], [B|Bs]) :-
eqs_lefts_rights(ABs, As, Bs).